1. Field of the Invention
This invention relates to encapsulated electronic circuits and, in particular, to shock-resistant electronic circuit assemblies that find use in blasting components.
2. Related Art
Electronic timing circuits for firing detonators after a predetermined, electronically-controlled delay period are known. The delay period is measured from the receipt of an initiation signal that may provide power for the timing circuit. Thus, U.S. Pat. No. 5,133,257 to Jonsson, issued Jul. 28, 1992, discloses an ignition system comprising a piezoelectric transducer that can be disposed next to a detonating cord branch line. When the detonating cord detonates, a shock wave is imposed on the piezoelectric transducer which then produces an electrical pulse. The electrical energy from the transducer is stored in a capacitor which provides power for a timer. After a predetermined delay, the timer allows the remaining stored energy in the capacitor to fire an ignition head in the detonator. The ignition head initiates explosive material, thus providing the explosive output for the detonator. Electronic delay circuits may also be used to initiate bridge elements such as a semiconductor bridge as described, e.g., in U.S. Pat. No. 4,708,060 to Bickes, Jr. et al, issued Nov. 24, 1987, or a tungsten bridge as described, e.g., in U.S. Pat. No. 4,976,200 to Benson et al, issued Dec. 11, 1990. Other electronic delay circuits are seen in U.S. Pat. No. 5,173,569 to Pallanck et al, issued Dec. 22, 1992; in U.S. Pat. No. 5,377,592 to Rode et al, issued Jan. 3, 1995; and in U.S. Pat. No. 5,435,248 to Rode et al, issued Jul. 25, 1995. These patents generally suggest that the electronic circuitry be molded within a suitable plastic package, casing or "potting compound". See, e.g., the Jonsson Patent at column 2, lines 42-50; the Pallanck et al Patent at column 3, lines 32-35; the Rode et al Patent (U.S. Pat. No. 5,377,592) at column 9, lines 30-33 and the Rode et al Patent (U.S. Pat. No. 5,435,248) at column 7, lines 9-13. The stated purpose for such enclosures is to protect the electronic components and minimize the chances of detonation or damage by mechanical impact. No particular configuration or material for such casings is disclosed in these patents.